52 



VETERINARY STUDIES 



waste materials unless it is brought in contact with air. It is 

 in the lungs that the red blood cells and serum load up with 

 oxygen, and it is here that carbon dioxid gas (CO,) and 

 other volatile impurities are eliminated from the blood. The 

 water, CO,, and other volatile compounds in the blood capil- 

 laries, and oxygen in the inspired air, are separated in the lungs 

 by a thin animal membrane. Nature is constantly endeavoring 

 there to equalize pressures and satisfy chemical affinities be- 

 tween free gases on one side of this membrane and gases held 

 by a liquid on the other side of this same membrane. 



i/VATER 



OXYGEN 



HEAT 



CARBON - Dl- OX/Dt 



LUNGS 



BLOOD 



GA5 



BODY T/SSUf^ 



Fig. 28. — Eespiration in Diagram. (M. E. E.) 



Aside from chemical combination, each gas moves either way 

 according to the partial pressure of the gas on one side and the 

 tension of the same gas in the liquid on the other side of this 

 membrane. The tension of the oxygen in venous blood is much 

 lower than oxygen pressure in lung air. The tension of COg 

 in the venous blood is much higher than its pressure in the lung 

 air. These variations in pressures and tensions do not appear 

 to account for all exchange. The living tisslie cells appear to 

 have a part and probably interfere with the perfect working of 

 these forces and a portion of the CO, is carried as carbonate 

 and bicarbonate of soda. 



The factors that vary the proportion of oxygen consumed 

 and CO, excreted are: body weight, amount of body surface, 

 also rate and depth of respiration. We have the lowest rate of 

 respiratory change in the body during fasting and highest rate 

 on a nitrogenous diet. 



The amount of oxygen absorbed and CO, developed increase 



